Add collections support to AccessKit atspi

[JasonTheKitten]

Hello,

I made a fork of AccessKit that includes support for collections in Atspi, needed for Orca Browsing Mode to work properly.

I'm marking this as a Draft PR, because it's not really polished to merge.

It adds the Collection interface with the following four methods:

• get_active_descendant
• get_matches (this is the one used by Orca)
• get_matches_to
• get_matches_from

The collection interface binding (as well as some atspi shim code) lives in adapters/unix/src/atspi/interfaces/collection.rs.

The actual matching logic is in a dedicated file called adapters/atspi-common/src/node_matcher.rs.

GetMatchesTo and GetMatchesFrom pass a direct object reference (instead of an index) over dbus. I couldn't figure out how existing code handled that, so I did add a helper utility (object_util.rs) to help with that; feel free to replace it with whatever your native method for doing this is.

There's a few reasons why I'm submitting this as a draft PR:

• It relies on RoleSet from atspi 0.31, which has not been published to crates yet, so need to wait on that
• atspi role matcher deserialization seems broken, so it uses a slightly hacky shim to work around that
• Because Orca's features like "Jump to Heading" rely on the node implementing Text to read back the content, and I don't have a full list of all such node types used by Orca, I've changed it to allow any node to have text runs for now
• There's an unwrap call that I forgot to remove
• I've only done manual testing (see document_browsing.rs, I also used a dbus mock call app for testing too). I've not written unit tests for it yet, and will not get around to it for a while.

Just figured I'd put my work here in case it is useful, could serve as reference if you decide to implement it differently.